It is known thanks to U.S. Pat. No. 4,833,405 a procedure for measuring the axial position of axes, comprising in its first type the use of two inductive probes in different axial positions and the machining of the cogwheel of the axis following two different angles with respect to the axial direction.
However, this system needs calibration for the correct identification of the axis position.
It also has problems of interaction with the magnetic field between the sensors, which is a problem that must be solved by means of the use of special sensors.
In the same patent a second procedure is described, also based on the use of two probes located in the same axial plane, but slightly separated, combined with the machining of the two opposite sloping ramps in each tooth.
This system enables to measure the axial displacement of the axis by the relation of the signal amplitude generated by each sensor, which will be function of the air gap between said sensor and the machined tooth. According to the axial position of the axis a sensor will generate more tension and the other less or vice versa.
As two sensors are needed in this system in order to compare the signal, calibration is needed in order to identify the exact position of the axis, since any tolerance in the sensor positioning (more or less mounting depth) directly implies an axial position error which can only be corrected through calibration.
Likewise, sensor manufacturing tolerances (field intensity, dimensions, etc,) imply a direct error in the measurement which can only be corrected through calibration.
Due to the unavoidable aging of the sensor elements, a difference in their response can be expected as time passes, which will require periodic calibration.
The carrying out of a calibration supposes a continuous and controlled rotation of the axis (in order to obtain a measurement signal) and a controlled axial displacement and measurement thereof, which is a situation that is hard to solve in applications such as aeronautics where once the axis is mounted it is expected to separate as much as possible the engine intervention intervals, and carrying out the calibration in a real work environment has serious limitations as it is necessary to measure with respect to a pattern and to carry out the entire displacement path.
Besides, any movement that implies a rotation which does not coincide with the theoretical axis will entail an error in the measurement as each sensor is in a different axial plane. This effect can be produced for example by a bending of the axis which causes that the centre thereof and the rotation centre do not coincide in all its length.
Another of the advantages of this system is that it needs a machined axis length of at least twice the maximum axial displacement to be measured, since said displacement must be measured by both probes located in different axial planes.
This system enables the measurement of the axis rotation speed with the necessary resolution in applications where the maximum pulses per turn are necessary.
Thanks to U.S. Pat. No. 5,198,763 it is known another procedure to measure the axial position of axes based on the time difference between the signal generated by machined teeth in the axis, one in the axial direction and another with a variable rotation with the axial position.
However, this system lacks the necessary amount of pulses per turn for an application where the answer vis-à-vis variations in the rotation speed is fundamental, and two pulses, unsynchronized, per turn entails a significant delay in detecting these variations.
On the other hand, this system complicates the usually simple and necessarily robust rotation pattern measurement system, as it has two pulses per turn the offset of which varies with the axial position.
U.S. Pat. No. 5,198,763 describes a procedure for measuring the axial position of axes, but this procedure requires the use of specific sensors for its functioning, which are very different from traditional inductive sensors used for measuring the rotation pattern.
This measuring procedure requires the use of eight sensors for its operation.
Thus, the axis length used for measuring is at least twice the average maximum displacement.
British patent No. 1,303,994 describes a procedure for measuring the axial position of axes, which requires the installation of a magnetic element in the rotation axis and wiring of particular characteristics in the stator.
This procedure generates a pulse per turn which is not enough for rotation pattern measuring systems requiring a fast response vis-à-vis speed variations.
This procedure is substantially different from the usual way of measuring the pattern using a cogwheel, usually having 60 teeth, in which case it is called trigger wheel.
British patent No. 2,181,246a describes a procedure for measuring the axial position of axes, which requires the installation of a magnetic element in the rotation axis and wiring of particular characteristics in the stator.
This procedure generates a pulse per turn which is not enough for rotation pattern measuring systems requiring a fast response vis-à-vis speed variations.
This system generates three pulses per turn with offsets proportional to the axial position, which complicates any pattern measuring system and makes the second and third pulse useless for measuring the rotation pattern.
This procedure is substantially different from the usual way of measuring the pattern using a cogwheel and, as such, it cannot be considered a compatible fast response pattern measurement system.
U.S. Pat. No. 3,190,125 describes a procedure for measuring the axial position of axes using the time difference between two pulses to determine the axial position.
This procedure requires such grounding of the rotating axis and of the measuring probe at a constant potential, and due to the variation of the capacitive effect due at the passage of the metal blades in front of the sensor elements there are obtained signal pulses the delay of which is proportional to the axial position.
This procedure generates a valid pulse per turn which is not enough for rotation pattern measuring systems requiring a fast response vis-à-vis speed variations. Since the second pulse is offset according to the axial position and it is not possible to use it for the pattern measurement. This is a system exclusively oriented towards measuring the axial position.